[cmake] Allow excluding additional include paths from being stored in dictionaries

[jmcarcell]

This Pull request:

Changes or fixes:

The include directories of external dependencies used by a library are stored in the includePaths[] of its dictionary, and they are added to the interpreter when the library is loaded. When ROOT and its dependencies are built in one place and then relocated, these paths no longer exist but still show up in gSystem->GetIncludePath(). For example, in the LCG nightlies, ROOT and its dependencies are built under /build/jenkins/... and then deployed to CVMFS:

-I"/build/jenkins/workspace/lcg_nightly_pipeline/install/dev3/pcre2/10.49/x86_64-el9-gcc15-opt/include"
-I"/build/jenkins/workspace/lcg_nightly_pipeline/install/dev3/xxHash/0.8.3/x86_64-el9-gcc15-opt/include"
-I"/build/jenkins/workspace/lcg_nightly_pipeline/install/dev3/tbb/2023.1.0/x86_64-el9-gcc15-opt/include"
-I"/build/jenkins/workspace/lcg_nightly_pipeline/install/dev3/jsonmcpp/3.12.0/x86_64-el9-gcc15-opt/include"

This adds ROOT_DICTIONARY_EXCLUDE_PATHS, a list of path prefixes that are passed to rootcling as -excludePath, so that include paths under them are not stored in the dictionaries (let me know if there is a better way of doing this). They are still used for parsing when generating the dictionaries. This is only useful for builds that are relocated, where the dependencies are found at runtime through the environment of the final installation (e.g. ROOT_INCLUDE_PATH). Nothing changes when the variable is not set. For the case above, it would be -DROOT_DICTIONARY_EXCLUDE_PATHS=/build/jenkins/workspace/lcg_nightly_pipeline/install/dev3.

Together with #23704, which does the same for the ROOT build directory, no build paths are left in gSystem->GetIncludePath().

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    24 files      24 suites   4d 0h 46m 7s ⏱️
 3 889 tests  3 886 ✅ 0 💤 3 ❌
83 234 runs  83 231 ✅ 0 💤 3 ❌

For more details on these failures, see this check.

Results for commit f3bf7c7.

♻️ This comment has been updated with latest results.